How to winterise your boat engine

There’s no doubt winter is upon us and only the people most resilient to cold weather will be out on the sea. If you’ve stopped going out on your boat then it is time to winterise your engine.

If your engines are still under warranty it is probably best to ask the company who gave you the warranty to service and winterise your boat engine or you could always instruct a local service supplier to do the work for you. 

No matter what sort of boat you have, all fuel systems will need some individual attention. Always start by referring to the engine manual. Even though winterising your engine shouldn’t be complicated, each manufacturer has slightly different methods and there may be some specific actions required for your engine model.

How to winterise an outboard engine

  1. Drain all the water from the cooling systems. Simply tilt the engine down as far as it will go and leave the engine to drain all the water.
  2. Protect the engine from corrosion. For older outboards, you will need to run fogging oil through the engine. For modern outboards, some manufacturers recommend products that can be mixed with petrol and then simply run through the engine. You may be lucky and your outboard may simply require you to switch the engine to “winterise” mode and press a button.
  3. Change the oil and fuel. Whilst you’re looking at your engine it’s also a good idea to change the oil and fuel so dirty oil and fuel aren’t sat in the engine all through the winter.
  4. Cover the engine. It’s a good idea to cover the engine to reduce dust and any knocks but always add fuel stabiliser and leave some ventilation so no condensation forms.
  5. Disconnect the battery, charge and store.

Many boat owners believe the best way to winterise an outboard is to run the engine every couple of weeks for long enough that the engine reaches normal operating temperature.  This is a valid view as problems with outboards are down to the outboard not being used rather than the effects of low temperatures. If you’re prepared to commit the time and are able to access and run your outboard engine through the winter then simply running the engine may be your best route.

How to winterise a stern drive engine

Winterising a stern drive engine can be more complicated than an outboard because you need to drain water from the engine block as well as the drive part of the engine.

  1. Drain all the water from the cooling systems. Remove all the block plugs and let the water and any sediment to drain out.
  2. Run antifreeze through the drive and engine.
  3. Protect the engine from corrosion. Run a fogging treatment through the engine. Make sure the engine is at a normal operating temperature so that any moisture is removed.
  4. Keep moving parts moving. Fill a grease gun with waterproof marine grease and lubricated all the fittings and wipe away any old hardened grease.
  5. Give the engine a check over. Look out for any parts which are showing wear and need to be replaced. Obvious parts to look at are hoses and clamps.
  6. Change the oil and fuel.  It’s always a good idea to remove dirty oil and fuel through the winter so there is less chance of sediment forming in the engine.
  7. Cover the engine.
  8. Disconnect the battery, charge and store.

How to winterise an inboard engine

Winterising an inboard engine is similar to a stern drive engine. The only difference is where a boat remains in the water for the winter you’ll need to run antifreeze through the engine by closing the intake seacock, removing the intake hose and putting it in a bucket of antifreeze.

Whilst you’re looking at the engine have a look at the propellor and the propellor shaft for any damage or debris. If you can, re-grease the prop shaft. 

Winterising a modern boat engine should be fairly straightforward, however many boat owners also take the opportunity to check over the engine for wear and tear. At this point many boat owners, particularly those who have invested in expensive engines, will use the services of a qualified marine mechanic.

    See a short video from on how to winterize your engine.  Of course, our door is open for any queries. How to Winterize a Four Stroke Outboard Motor

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